It is common to retread worn vehicular tires so that the tires may be reused. Typically, a tire carcass is inspected prior to applying a new tread portion in order to detect any flaws in the carcass, such as a defect in the inner liner, that would make the carcass unsuitable for retreading.
Visual inspection of a tire carcass to detect flaws has been known for many years, and is typically employed as one part of the inspection before retreading. Visual inspection, however, while useful for detecting gross flaws in tire carcasses being evaluated for possible retreading, is not suited for reliably detecting certain flaws. In particular, flaws that involve a defect too fine or too obscure to detect visually may be inadvertently overlooked and retreaded to produce a defective retreaded tire.
Various testing devices and methods have been developed to supplement visual inspection methods during the tire retreading process. Some prior methods, such as disclosed in U.S. Pat. Nos. 4,297,876 and 4,327,579 each of which is fully incorporated herein by reference, involve the use of ultrasonic energy. Other methods, such as described in U.S. Pat. Nos. 6,304,090 and 4,520,307, which are owned by the owner of the present invention and which are also incorporated fully herein by reference, involve the use of high potential electrical energy.
In the method described in U.S. Pat. No. 6,304,090, a testing head that carries a high voltage is applied to the interior surfaces of a tire being tested. A corresponding grounding element, which may be part of a tire spreader or tire rotating device, is applied to the outside of the tire opposite the testing head. This grounding element is maintained at substantially ground potential. Flaws are detected by arcing between the testing head and the grounding element through the flaw.
Generally, with prior testing devices, if the testing head is made large enough to cover a significant area of the inner surface of the tire so that testing can be accomplished in one rotation of the tire, the beads of tire must be spread apart to enlarge the access opening to facilitate insertion of the testing head. Further, the beads of the testing head must be spread again for removal of the testing head. Special equipment may be required for spreading the beads of the tire, presenting an additional cost and requiring additional time for testing each tire.
Also, the testing head and the grounding element are generally positioned on opposite sides of the tread portion of the tire in prior devices. The inner liner, the reinforcing cords and the tread portion of the tire are all positioned in series between the testing head and the grounding element. Flexibility and ease of use of the equipment is limited, since the elements must be carefully maintained in position on the inside and outside of the tire. Also, relatively high electrical potentials are used in prior devices to overcome the impedance presented by such an arrangement, resulting in costly equipment components. Even with such higher potentials, smaller defects may sometimes go undetected.
There is a need in the industry for an electrical tire testing system that overcomes the above identified issues presented by prior art devices and methods.